Conventionally, as an ultraviolet-shielding agent used for cosmetics, inorganic ultraviolet-shielding agents and organic ultraviolet absorbents have been selectively used depending on use. Since different kinds of inorganic ultraviolet-shielding agents and organic ultraviolet absorbents can shield different wavelengths of ultraviolet rays, cosmetic preparations have been formulated by appropriately combining inorganic ultraviolet-shielding agents and organic ultraviolet-shielding agents.
Particularly, since inorganic ultraviolet-shielding agents scatter or reflect ultraviolet rays using physical mechanisms, inorganic ultraviolet-shielding agents have a small influence on skin, and are used in sun-screening for a wide range of users from infants to adults.
Preferable examples of the inorganic ultraviolet-shielding agents include zinc oxide, titanium oxide and the like which have a high opacifying power with respect to ultraviolet rays and are also used as white dyes.
However, in a case in which zinc oxide or titanium oxide was applied to cosmetic preparations, when the average dispersed particle diameter was 0.1 μm or more, there were problems in that cosmetic preparations were whitened so as to degrade transparency, and natural makeup could not be obtained.
In addition, it is difficult to disperse zinc oxide or titanium oxide in cosmetic preparations in an average dispersed particle diameter of 0.1 μm or less. In addition, even when zinc oxide or titanium oxide could be dispersed, such zinc oxide or titanium oxide had a high surface activity, and provided a rough feeling when coming into contact with skin. In addition, in a case in which the primary particle diameter or average dispersed particle diameter in cosmetic preparations of zinc oxide or titanium oxide was large, there was a problem in that the transparency of cosmetic preparations was degraded.
Meanwhile, organic ultraviolet absorbents chemically absorb energy, and convert the energy into thermal energy, thereby preventing ultraviolet rays from intruding into skin cells. In addition, when compared with inorganic ultraviolet-shielding agents, organic ultraviolet absorbents produce a high ultraviolet-shielding effect even in a small amount, and are used for adult sun-screening. Compared with inorganic ultraviolet-shielding agents, organic ultraviolet absorbents do not become white when coated on skin and have an advantage of a high transparency.
Examples of the organic ultraviolet absorbents include dibenzoylmethane-based compounds, benzophenone derivatives, para-aminobenzoic acid derivatives, methoxycinnamic acid derivatives, salicylic acid derivatives and the like, and, in particular, as a UVA absorbent that absorbs near ultraviolet rays, a dibenzoylmethane-based compound, particularly, 4-tert-butyl-4′-methoxydibenzoylmethane (avobenzone) is widely used.
However, since organic ultraviolet absorbents are insoluble in water, it was necessary to dissolve an organic ultraviolet absorbent in a specific non-aqueous solvent in order to exhibit the ultraviolet absorbing effect, and therefore limited kinds of solvents could be used, which created a problem of a decrease in the degree of freedom as cosmetic preparations. Furthermore, when anon-aqueous solvent was mixed with a cosmetic preparation, there was a problem of the occurrence of a sticky feeling.
Furthermore, when an inorganic ultraviolet-shielding agent and an organic ultraviolet absorbent are jointly used, there is a concern that the organic ultraviolet absorbent may be recrystallized due to the influence of metallic ions included in the inorganic ultraviolet-shielding agent such that the qualities or colors of cosmetic preparations may be changed, and the feeling of use of cosmetic preparations may degrade. As described above, there was a problem in that an inorganic ultraviolet-shielding agent and an organic ultraviolet absorbent could not be freely mixed when formulating a cosmetic preparation.
Therefore, in order to solve the above problems, resin powder, which is highly transparent, excellent in terms of feeling in use, and has an average particle diameter of 0.1 μm to 1 μm, obtained by including metallic oxide particles having an ultraviolet-shielding function in an acryl-based resin is proposed (PTL 1).
In the resin powder, since direct contact between the organic ultraviolet absorbent and the metallic oxide is prevented, the recrystallization and the like of the organic ultraviolet absorbent are suppressed.
In addition, as resin powder that suppresses the dermal irritancy of an organic ultraviolet absorbent, resin powder including a core portion made of a (meth)acryl-based resin containing an organic ultraviolet absorbent, which is formed by dispersing a monomer that forms the (meth)acryl-based resin in which the organic ultraviolet absorbent is dissolved in an aqueous medium and causing a polymerization reaction, and a surface layer portion made of a (meth)acryl-based resin which is formed on a surface of the core portion and does not contain the organic ultraviolet absorbent is proposed (PTL 2).
In the resin powder, since direct contact between the organic ultraviolet absorbent and a metallic oxide is prevented, the recrystallization and the like of the organic ultraviolet absorbent are suppressed.